1. Field of the Invention
The present invention relates to a method for driving a flat panel display and a driving circuit therefor, and, particularly, to a novel method for driving an X-Y dot matrix type AC-refresh plasma display panel which is effective to realize an increased display area with minimized power consumption, and a driving device for use in performing the same.
2. Description of the Related Art Including Information Disclosed Under Section 1.97 - 1.99
The plasma display device utilizes discharge phenomenon of rare gas and, in view of a recent strong demand of its application to a thin and lightweight displays for office and/or industrial automation, deligent efforts are being made to realize such devices as having a large display area and make them commercially available. The plasma display panel (PDP) can be classified generally into a d.c. type which utilizes d.c. discharge and an a.c. type which utilizes an a.c. discharge. Among the a.c. type panels, those in which display informations are stored as wall charge within the panel and then displayed are referred to as being of a memory type and those in which informations stored in an external memory are read out and displayed repeatedly are referred to as being of a refresh type, the both having respective features.
Among those plasma display panels, the a.c.-refresh type PDP is advantageous in that a structure thereof is simple and legibility, reliability and life-time are superior to the other. Luminance of the a.c.-refresh type PDP depends upon the number of light emissions of each discharge cell, i.e., the number of a.c. voltage pulses applied thereto. A conventional driving system for the refresh type X-Y dot matrix display panel is schematically shown in FIG. 1, in which line-at-a-time scanning system is employed. Scanning electrodes (line electrodes Y.sub.l . . . Y.sub.n) are sequentially selected by a scanning circuit 21 and a required series of high voltage pulses are applied thereto during each period of selection. At the same time, a series of high voltage pulses opposite in phase to the voltage pulses applied to the scanning electrodes are supplied from column electrodes (X.sub.l . . . X.sub.m) according to a data signal from an image data signal input circuit 22 and cells each located at a cross point of the both electrodes illuminate proportionally to the number of the applied pulses. Incidentally, V.sub.SC and V.sub.DA in the same figure depict power sources for the scanning circuit 21 and the image data signal input circuit 22, respectively. For a PDP having a large display area, however, the number of scanning electrodes required is at least 400. In order to obtain a satisfactory display luminance of such large PDP, it is necessary to increase a panel drive frequency correspondingly to the number of scanning electrodes. In fact, assuming that, in order to obtain such satisfactory display luminance, it is necessary to apply a.c. pulses at a rate of 2000 pulses/second to each display cell, a drive frequency required for such panel having 400 scanning electrodes becomes 2000.times.400=800 (KHz). Since a voltage necessary for gas discharge is usually 120-150 V (in either side), a high frequency and high voltage are required to drive such large a.c.-PDP, resulting in problems of making the conventional driving circuit possible to use higher frequency with reduced power consumption.
In view of such problems, uses of a high speed, high voltage CMOS driver which may be usable instead of the conventional high voltage bipolar driver and an unbalanced drive system in which a drive voltage on a scanning side is made as high as possible and a driving voltage on a data side is made as low as possible have been proposed by Sakuma et al. in "An AC Refresh PDP with High Voltage CMOS Drivers and Unbalanced Power Supplies", No. 7.5, page 99, Society for Information Display (SID)84 DIGEST, 1984. According to the proposition, a large area PDP with 400 scanning electrodes.times.640 data electrodes, for instance, has been realized with a less power consumption of about one tenth that of the conventional method.
Also, in the recent information-oriented society, there is an increased demand of a display device whose power consumption is low enough to make it usable with a battery and whose display capability is much more improved. In order to drive such PDP with a battery, it has to operate with a power of several Watts at most. On the other hand, as to the display area, a realization of display panel containing a large number, say, 1000 to 2000, of scanning electrodes, is being required. When, for instance, the number of electrodes of a 400.times.640 dot display panel is doubled to realize a 800.times.1280 dot panel, the number of display dots becomes four times that of the 400.times.640 dot panel. Even if a scanning is possible by using a high speed CMOS driver, the power consumption of the panel may be increased at least four times due to increased driving frequency and increased load capacitance. Since, on the side of scanning electrodes which are driven line by line, the number of electrodes becomes twice and the load capacitance for each electrode becomes twice, the power to be consumed in the drive circuit becomes four times. On the other hand, on the data electrode side, frequency, the number of electrodes and load capacitance for each electrode are twice, respectively. Therefore, the power to the drive circuit becomes 8 times. Since the driving power on the data side of the a.c.-refresh PDP in which all electrodes are driven simultaneously is larger than that on the scanning side, the power consumption of the whole PDP when the display area is doubled is not 4 times but substantially 8 times.